The present invention relates to a vacuum interrupter, particularly to the vacuum interrupter in which two separable electrical contacts are surrounded by a vacuum envelope including a cylindrical metallic housing and insulating end plates provided at opposite ends of the housing.
This kind of vacuum interrupter was invented by Sakuma et al., the present inventors, and was first disclosed in the co-pending U.S. patent application Ser. No. 276,862 filed on June 24, 1981.
The vacuum interrupter of this kind is manufactured as follows; first, temporary assembly of the vacuum interrupter is performed by accurately positioning the members of the interrupter with the aid of a jig such that solid brazing material of a certain thickness has been fitted into the clearances between surfaces which are to be joined of the vacuum interrupter, and then, the temporarily assembled vacuum interrupter is brazed into vacuum-tightness in a vacuum furnace.
Two surfaces to be joined of the vacuum interrupter are directly exposed to a chamber to be maintained vacuum-tight (hereinafter referred to a vacuum chamber of the interrupter). In addition, with regard to material, the insulating end plates, may be made of ceramics such as, for example, aluminum oxide ceramics Al.sub.2 O.sub.3, which has a relatively large heat emissivity, that is, will increase rapidly in temperature during heating, and drop in temperature rapidly during cooling.
Therefore, vaporized brazing material will tend to disperse throughout the vacuum chamber of the interrupter during heating in the vacuum furnace and will be deposited on the interior surfaces of the insulating end plates during the slow cooling process. This increases the electrical conductivity of the insulating end plate which greatly lowers the vacuum surface withstand voltage of the end plate.